There are several types of well water filtration designed to remove various contaminants. Different methods are capable of removing different sets of impurities, but no filter type can remove all possible contaminants. Therefore, it is important to know which substances are present before choosing a filtration system.

One of the most common reasons to treat well water is to remove iron and manganese, which often leach into groundwater from the surrounding soil and rocks. Iron and manganese, at levels usually found in well water, are not health hazards, but too much can give a reddish-brown tint to the water and stain laundry, bathtubs, and sinks. Nitrogen and hydrogen sulfide are occasionally found in well water as well. Hydrogen sulfide causes an odor similar to rotten eggs, while too much nitrate can cause methemoglobinemia, commonly called blue baby disease. Well water filtration is usually not used for bacterial contamination, as groundwater generally has very low concentrations of bacteria.

Some common filter materials include granular activated carbon (GAC), manganese greensand, and BIRM. GAC is processed to give it a high surface area, which causes it to have high absorptivity. It can trap a variety of contaminant particles, including iron, manganese, hydrogen sulfide, and chlorine. A disadvantage of GAC is that it must be replaced regularly.

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Manganese greensand is used to remove iron and manganese from water. Glauconite, the active material in manganese greensand media, reacts with soluble iron and manganese to form insoluble versions of these substances, which are trapped in the filter material. Manganese greensand functions in high concentrations of iron and manganese, and completely removes the contaminants. Regular maintenance is generally required to keep the filter operating properly.

BIRM is another filter material that is mainly used to remove iron and manganese. It catalyzes the reaction between iron or manganese and oxygen. The oxidation process forms insoluble iron and manganese, which is then trapped by the filter. This type of well water filtration also requires regular maintenance to clean the filtering material.

Anion exchange and ion exchange, also known as water softening, are two similar treatment methods that work to remove different contaminants. Both methods remove contaminant particles as water passes through a charged resin bed. Ion exchange uses a negatively-charged material to capture positively-charged ions, including iron, manganese, calcium, and magnesium, while anion exchange uses a positively-charged resin to capture negatively-charged ions including nitrate, sulfate, and fluoride. Both types of treatment may cause water to become corrosive and increase its sodium content.

Reverse osmosis (RO) is a well water filtration method that uses a selective membrane. Pressure is used to force water through this thin material, leaving contaminants on one side while purer water comes through. RO can remove a wide variety of contaminants, including iron, manganese, nitrate, sulfate, sodium, fluoride, chloride, heavy metals, and some organic materials. On the other hand, reverse osmosis is often not a viable option for household treatment systems, as RO units are expensive and require large amounts of water.

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